Resistance to Frequency Converter

Amol Mupid

Andrew Ricketts

Outline Original design

Component parts Roadblock

Modified design Buffer optimization

Design specification Conclusion

400

Chemiresistive Sensors

αACsR1=

Rs

Rs : resistance of nanowire

C : concentration of the gas

A,α : constants that change with type of gas and temperature

350

Original design

D

CLK

Q

Qbar

+

-

-

+

Rs

Vout

R4

R1

R2

R3 C

R5

Original design components Diode

Spice simulation …but layout issues insurmountable

Original design components Zener Diode

More simulations possible …but layout even more challenging

Modified design Key point is that what is desired is a

way to control oscillations based on input voltage Voltage Controlled Oscillator (VCO)

Buffer added to output to ensure rapid rise and fall of output square wave

VCO design LC tank oscillators

Good phase noise with low power but tuning range is relatively low Output frequency may fall out of range due to

process variations Spiral inductors occupy a lot of area, high cost and

low yield issues. Ring oscillators

Easy integration, high yield, low cost. Less chip area In-phase outputs

Single delay cell

Schematic of rectified VCO

Buffer optimization Initial single stage buffer

Moved output close to binary Had difficulty clamping small swings about

origin Double stage buffer

Delay increase inconsequential Greatly improved clamping range

Layout of complete design

Transistor sizing

Core area 48.75 X162.6 = 7,926(um^2)

Transistor Width (um) Length (um)

Mb1 11.0 0.6

Mp1,Mp2 5.16 0.6

Mp3,Mp4 5.16 0.6

Mn1,Mn2 3.0 0.6

MpInv 18.0 0.6

MnInv 6.0 0.6

Voltage dependant output periodicity

0

0.5

1

1.5

2

2.5

3

period(NS)

frequency(GHz)

3.3V3.5V4V4.5V5V

Power dissipation ( mW)

0

5

10

15

20

25

30

max power avg power rms power

3.3v3.5V4V4.5V5V

Resistance We want the Vcontrol be to

be in between operable range

=> Rs*VDD/ (Rs+ R) has to be in between 3.3V and 5V

Rs

R

Vcontrol

Conclusion The change in the sensor resistance

can be detected in “ns” range and converted to square wave pulses

This completely eliminates the need of ADC, huge potential resource savings.

Successfully overcame practical design issues and produced desired results.

Thank You

Questions??